Polishing composition and method for producing same

ABSTRACT

Provided is a polishing composition which contains a water-soluble polymer and is suitable for reducing LPDs. The polishing composition provided in this application includes an abrasive, a water-soluble polymer, and a basic compound. In the polishing composition, the content of a reaction product of a polymerization initiator and a polymerization inhibitor is 0.1 ppb or less of the polishing composition on a weight basis.

TECHNICAL FIELD

The present invention relates to a polishing composition and a methodfor producing the same.

The present application claims priority to Japanese Patent ApplicationNo. 2017-214204, filed on Nov. 6, 2017, and the entire contents thereofare incorporated herein by reference.

BACKGROUND ART

A polishing process called chemical mechanical polishing (CMP) is widelyused as a technique for smoothing a silicon wafer (hereinafter simplyreferred to as a wafer). A polishing composition containing fineabrasive particles and a basic compound is used in CMP. In the CMPprocess, mechanical polishing with such an abrasive and chemicalpolishing with a basic compound proceed simultaneously, and thus a widerange of surface of a wafer can be smoothed with high precision.

Generally, in a wafer polishing process according to CMP, 3- to 4-steppolishing is performed to realize high precision smoothing. In the firsthalf of the polishing process, mainly for rough polishing, a highpolishing removal rate tends to be required. On the other hand, thelatter half of the polishing process is mainly for finishing the waferto have a smoother surface with higher quality. A method using apolishing composition containing a water-soluble polymer is known as amethod for obtaining a highly smooth surface (Patent Document 1 to 3).

CITATION LIST Patent Document

-   [Patent Document 1] Japanese Patent Application Publication No.    2004-128089-   [Patent Document 2] WO 2014/148399-   [Patent Document 3] WO 2014/196299

SUMMARY OF INVENTION Technical Problem

Along with further miniaturization of a semiconductor wiring, it isdesired to further reduce the number of micro defects generally calledlight point defects (LPDs), as well as to obtain high smoothness. Here,an object of the present invention is to provide a polishing compositionwhich contains a water-soluble polymer and is suitable for reducingLPDs. Another related object is to provide a method for producing such apolishing composition.

Solution to Problem

The inventors have focused on that there may be a product of thereaction (hereinafter simply referred to as a “reaction product”) of apolymerization inhibitor derived from a monomer or the like used as araw material and a polymerization initiator in a polishing compositioncontaining a water-soluble polymer. The inventors found that limitingthe content of the reaction product to a certain value or less iseffective in reducing LPDs, and completed the present invention.

A polishing composition provided in this specification includes anabrasive, a water-soluble polymer, and a basic compound. In thepolishing composition, a content of a reaction product of apolymerization initiator and a polymerization inhibitor is 0.1 ppb orless of the polishing composition on a weight basis. Such a reactionproduct is likely to be adsorbed on the surface of an object to bepolished, and may cause the generation of LPDs. When the content of thereaction product is reduced to 0.1 ppb or less, the generation of LPDsdue to adsorption of the reaction product is prevented, and LPDs can bereduced as a whole.

In addition, in this specification, provided is a method for producingany of the polishing compositions disclosed herein. The method includespreparing a polymer composition containing the water-soluble polymer.Here, a content of the reaction product in the polymer composition is0.1 ppb or less with respect to the polishing composition on a weightbasis. The method further includes mixing the polymer composition, theabrasive, and the basic compound. With the use of the polymercomposition in which the content of the reaction product is limited to adesignated value or less, it is possible to appropriately produce apolishing composition disclosed herein.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention will be described below.Matters necessary to implement this invention other than thosespecifically referred to in this specification may be understood asdesign matters to a person of ordinary skill in the art based on theconventional art in the pertinent field. The present invention can beimplemented based on the content disclosed herein and common technicalknowledge in the field.

As used herein. “(meth)acrylic” comprehensively refers to acrylic andmethacrylic, and “(meth)acrylate” comprehensively refers to acrylate andmethacrylate. Similarly, “(meth)acryloyl group” comprehensively refersto an acryloyl group and a methacryloyl group.

<Abrasive>

A polishing composition disclosed herein contains an abrasive. Theabrasive has a function of mechanically polishing a surface of an objectto be polished.

The abrasive is not particularly limited, and various known abrasivethat can be used in polishing composition for objects to be polishedsuch as wafers can be used. Examples of such abrasives include silicaparticles, inorganic particles other than silica particles, organicparticles, and organic-inorganic composite particles. One type ofabrasive can be used or two or more types of abrasives can be used incombination.

The abrasive in the art disclosed herein, inorganic particles arepreferable, and among these, particles composed of an oxide of metal ormetalloid are preferable, and silica particles are particularlypreferable. In polishing of an object to be polished having a surfacemade of silicon such as a silicon substrate, for example, in a polishingcomposition that can be used for finish polishing, it is particularlysignificant to use silica particles as the abrasive. The art disclosedherein can be preferably implemented in an embodiment in which theabrasive substantially consists of silica particles. Here.“substantially” means that 95 wt % or more, preferably 98 wt % or more,or more preferably 99 wt % or more of particles constituting theabrasive are silica particles, and includes the case in which 100 wt %thereof are silica particles.

Specific examples of silica particles include colloidal silica, fumedsilica, and precipitated silica. Silica particles can be used singly orin a combination of two or more. Colloidal silica is particularlypreferably used because it tends to facilitate obtaining a polishedsurface having excellent surface quality after polishing. As thecolloidal silica, for example, colloidal silica obtained from waterglass (sodium silicate) as a raw material using an ion exchange method,or alkoxide-method colloidal silica can be preferably used.Alkoxide-method colloidal silica is colloidal silica produced accordingto a hydrolysis and condensation reaction of an alkoxysilane. Colloidalsilicas can be used singly or in a combination of two or more.

The average primary particle size of the abrasive is not particularlylimited. In consideration of a polishing removal rate and the like, itis preferably 5 nm or more, and more preferably 10 nm or more. In viewof improving the polishing effect, for example, it is preferably 15 nmor more, more preferably 20 nm or more, and still more preferably morethan 20 nm. In addition, in view of improving the smoothness, theaverage primary particle size of the abrasive is preferably 100 nm orless, more preferably 50 nm or less, and still more preferably 40 nm orless.

Here, the average primary particle size in this specification is aparticle size calculated from a specific surface area (BET value)measured by a BET method according to the formula of average primaryparticle size [nm]=6,000/(true density [g/cm⁻³]×BET value [m²/g]). Forexample, in the case of silica particles, the average primary particlesize can be calculated according to the average primary particle size[nm]=2,727/BET value[m²/g]. The specific surface area can be measuredusing, for example, a surface area measuring device, product name “FlowSorb II 2300” available from Micromeritics Instrument Corporation.

The average secondary particle size of the abrasive is not particularlylimited, and can be appropriately selected from, for example, a range ofabout 10 nm to 500 nm. In consideration of a polishing removal rate andthe like, the average secondary particle size of the abrasive may be,for example, 15 nm or more, 20 nm or more, or 30 nm or more. In view ofimproving the polishing effect, in some embodiments, the averagesecondary particle size of the abrasive may be 35 nm or more, 40 nm ormore, or more than 40 nm. In view of improving the smoothness, theaverage secondary particle size of the abrasive is generallyappropriately 200 nm or less, preferably 150 nm or less, and morepreferably 100 nm or less. In order to facilitate obtaining a higherquality surface, in some embodiments, the average secondary particlesize of the abrasive may be 75 nm or less or 70 nm or less. Here, theaverage secondary particle size of the abrasive in this specification isthe average particle size measured based on a dynamic light scatteringmethod. The average particle size can be measured using, for example,model “UPA-UT151”, available from Nikkiso Co., Ltd.

The shape (outer shape) of particles constituting the abrasive, alsoreferred to as abrasive particles hereinafter, may be globular ornon-globular. Specific examples of non-globular particles include apeanut shape, a cocoon shape, a konpeito shape, and a rugby ball shape.The peanut shape herein refers to a peanut shell shape. For example, anabrasive in which most of particles have a peanut shape or a cocoonshape can be preferably used.

Although not particularly limited, the average aspect ratio of theabrasive, that is, the average value of ratios of major axis/minor axisof the particles constituting the abrasive is, in principle, 1.0 ormore, preferably 1.05 or more, and more preferably 1.1 or more. Higherpolishing efficiency can be realized by increasing the average aspectratio. In view of reducing scratches and the like, the average aspectratio of the abrasive is preferably 3.0 or less, more preferably 2.0 orless, and still more preferably 1.5 or less.

The shape (outer shape) and average aspect ratio of particlesconstituting the abrasive can be determined by, for example, observationunder an electron microscope. In a specific procedure of determining anaverage aspect ratio, for example, using a scanning electron microscope(SEM), the smallest rectangles circumscribing particle images are drawnfor a predetermined number of abrasive particles whose particle shapescan be independently recognized. The predetermined number is, forexample, 200. Then, regarding the rectangles drawn for the particleimages, the lengths of the long sides are defined as values of the majoraxes, the lengths of the short sides are defined as values of the minoraxes, and values obtained by dividing the values of the major axes bythe values of the minor axes are calculated as ratios of majoraxis/minor axis of the particles, that is, aspect ratios. The averageaspect ratio can be obtained by arithmetically averaging the aspectratios of the predetermined number of particles.

The content of the abrasive in the composition can be appropriatelyselected in consideration of the type of the abrasive, a polishingremoval rate and a dispersion stability. For example, the content of theabrasive can be 0.001 wt % or more and 10 wt % or less with respect tothe total weight of the composition. The content can be 0.01 wt % ormore and 5 wt % or less, and can further be 0.1 wt % or more and 1 wt %or less. When the content of the abrasive is 0.001 wt % or more, forexample, a polishing removal rate of mechanical polishing can besecured, and when the content of the abrasive is 10 wt % or less, thedispersion stability of the abrasive can be secured. As will bedescribed below, the content of the abrasive can be preferably appliedto the content in a working slurry supplied to the object to bepolished.

<Water-Soluble Polymer>

The water-soluble polymer is not particularly limited, and a knownwater-soluble polymer that can be used in a polishing composition can beappropriately selected and used. Examples of water-soluble polymersinclude cellulose derivatives, starch derivatives, polymers including anoxyalkylene unit, vinyl alcohol-based polymers, acrylic acid-basedpolymers, and nitrogen-atom-containing polymers. Examples of cellulosederivatives include nitrocellulose, acetyl cellulose, and carboxymethylcellulose. Examples of starch derivatives include amylose, amylopectin,and pullulan as well as starch. Examples of polymers including anoxyalkylene unit include random copolymers and block copolymers ofethylene oxide and propylene oxide, and polyethylene glycol. Here, thevinyl alcohol-based polymer is a polymer having a structural partrepresented by the following chemical formula: —CH₂—CH(OH)—; as arepeating unit (hereinafter referred to as a VA unit) constituting thepolymer. The VA unit can be produced by, for example, hydrolysis (alsoreferred to as saponification) of a repeating unit of a structureobtained by vinyl polymerization of a vinyl ester type monomer such asvinyl acetate. A polymer generally called as a polyvinyl alcohol isencompassed in the concept of the vinyl alcohol-based polymer disclosedherein. The degree of saponification of the polyvinyl alcohol can be,for example, about 93% to 99%, but is not particularly limited. Inaddition, a polymer having a non-vinyl alcohol unit (hereinafterreferred to as a non-VA unit) in addition to the VA unit can be used asa vinyl alcohol-based polymer disclosed herein. The non-VA unit can be arepeating unit having at least one structure selected from the groupconsisting of hydrocarbon groups such as an alkyl group, an allyl ethergroup, an aryl group, an arylalkyl group, and a styrene group:oxyhydrocarbon groups such as an alkoxy group, an aryloxy group, anarylalkyloxy group, and an oxyalkylene group; and a carboxy group, asulfo group, an amino group, a hydroxy group, an amide group, an imidegroup, an imino group, an amidino group, an imidazolino group, a nitrilegroup, an ether group, an ester group, and salts thereof. The molarratio of VA units:non-VA units can be, for example, about 70:30 to 99:1,but are not particularly limited. Otherexamples of water-solublepolymers include polyisoprene sulfonic acid, polyvinyl sulfonic acid,polyallyl sulfonic acid, polyisoamylene sulfonic acid, polystyrenesulfonate, polyacrylate, and polyvinyl acetate. Water-soluble polymerscan be used singly or in a combination of two or more.

In some embodiments of the art disclosed herein, as the water-solublepolymer, a nitrogen-atom-containing polymer can be preferably used.Examples of nitrogen-atom-containing polymers include a polymer having astructural unit derived from a monomer having a nitrogen atom in themolecule. Examples of a monomer containing nitrogen atoms in themolecule (hereinafter referred to as a nitrogen-containing monomer)include N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine,(meth)(di)isopropylacrylamide, N,N-dimethyl(meth)acrylamide, andN-hydroxyethyl(meth)acrylamide. Nitrogen-atom-containing polymers maycontain, for example, 10 mol % or more and 100 mol % or less, 30 mol %or more and 100 mol % or less, 50 mol % or more and 100 mol % or less,more than 50 mol % and 100 mol % or less, or 70 mol % or more and 100mol % or less of one or two or more types of structural units derivedfrom such a nitrogen-containing monomer. Herein, the expression that anitrogen-atom-containing polymer includes X mol % or more of structuralunits derived from the nitrogen-containing monomer means that the numberof structural units derived from the nitrogen-containing monomer among atotal number of repeating units constituting thenitrogen-atom-containing polymer is X % or more.

Among these, a polymer having a structural unit derived fromN-(meth)acryloylmorpholine (hereinafter referred to as a morpholinepolymer) can be preferably used. Such a structural unit hashydrolyzability that is sufficiently suppressed under alkalineconditions, and has excellent usability. For example, it can avoidhydrolysis almost 100% at a pH of 10.0 and a temperature of 25° C. forat least 2 months. In addition, such a structural unit exhibitsappropriate adsorption properties with respect to abrasives or wafers.Therefore, even if a water-soluble polymer mainly composed of thestructural unit forms a polishing composition together with a basiccompound and the like, it exhibits excellent alkali resistance andexhibits favorable etching resistance. In addition, even if a polymerhaving such a structural unit has a high molecular weight (for example,a weight average molecular weight of about 600.000 or more), an abrasivesuch as silica particles can be favorably dispersed.

The morpholine polymer preferably has 10 mol % or more and 100 mol % orless of structural units derived from N-(meth)acryloylmorpholine. In themorpholine polymer, the amount of the structural unit derived fromN-(meth)acryloylmorpholine is more preferably, for example, 20 mol % ormore, 30 mol % or more, 40 mol % or more, or 50 mol % or more, and stillmore preferably, more than 50 mol %, 60 mol % or more, 70 mol % or more,80 mol % or more, 90 mol % or more, 95 mol % or more, 98 mol % or more,99 mol % or more, or 100 mol %. In some embodiments, a morpholinepolymer having a structural unit derived from N-(meth)acryloylmorpholinein a range of, for example, 50 mol % or more and 100 mol % or less,preferably 70 mol % or more and 100 mol % or less, and more preferably90 mol % or more and 100 mol % or less can be used.

In addition to such a structural unit, the morpholine polymer may have astructural unit derived from other monomers that can copolymerize withN-(meth)acryloylmorpholine. The other monomers are not particularlylimited, and examples thereof include (meth)acrylic acid alkyl esterssuch as methyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylateand 2-ethylhexyl(meth)acrylate; unsaturated acids such as (meth)acrylicacid, crotonic acid, maleic acid, itaconic acid and fumaric acid, andalkyl esters thereof; unsaturated acid anhydrides such as maleicanhydride; sulfonic acid group-containing monomers such as2-acrylamido-2-methylpmpanesulfonic acid and salts thereof;N-alkyl(meth)acrylamides such as methyl(meth)acrylamide,ethyl(meth)acrylamide, n-propyl(meth)acrylamide,isopropyl(meth)acrylamide, n-butyl(meth)acrylamide, and2-ethylhexyl(meth)acrylamide; (di)alkylaminoalkylamides such asmethylaminopropyl(meth)acrylamide, dimethylaminopropyl(meth)acrylamide,ethylaminopropyl(meth)acrylamide and diethylaminopropyl(meth)acrylamide;(di)alkylaminoalkyl(meth)acrylates such asmethylaminoethyl(meth)acrylate, dimethylaminoethyl(meth)acrylate,ethylaminoethyl(meth)acrylate and diethylaminoethyl(meth)acrylate;aromatic vinyl compounds such as styrene, vinyl toluene and vinylxylene; alkyl vinyl ethers having an alkyl group having 1 to 10 carbonatoms such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinylether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether,t-butyl vinyl ether, n-hexyl vinyl ether, 2-ethylhexyl vinyl ether,n-octyl vinyl ether, n-nonyl vinyl ether and n-decyl vinyl ether, vinylester compounds such as vinyl formate, vinyl acetate, vinyl propionate,vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinylbenzoate, vinyl pivalate and vinyl versatate; and α-olefins such asethylene, propylene, and butylene. The other monomers can be used singlyor in a combination of two or more.

The amount of the other monomers used in the morpholine polymer can be,for example, in a range of 0 mol % or more and 90 mol % or less, and maybe in a range of 0 mol % or more and 50 mol % or less, 0 mol % or moreand 30 mol % or less, 0 mol % or more and 20 mol % or less, or 0 mol %or more and 10 mol % or less. When the amount of the other monomers usedexceeds 50 mol %, the amount of N-(meth)acryloylmorpholine used is lessthan 50 mol %, and therefore the balance of the adsorption propertybetween the abrasive and the wafer is deteriorated and the surface ofthe object to be polished may not be finished smoothly.

A water-soluble polymer is commercially available or can be obtained bya known method, including the case in which the water-soluble polymer isa morpholine polymer. For example, the water-soluble polymer can beobtained by polymerizing monomers described above.

The polymerization method is not particularly limited, but a solutionpolymerization method is preferable because it enables to obtain awater-soluble polymer in a uniform state. It is preferable to obtain awater-soluble polymer by radically polymerizing monomers according to asolution polymerization method. Regarding a polymerization solvent forsolution polymerization, any of water, an organic solvent, and a solventmixture of water and an organic solvent can be used. Specific examplesof organic solvents include methanol, ethanol, isopropanol, acetone, andmethyl ethyl ketone. These can be used singly or in a combination of twoor more. Generally, water, or a solvent mixture of water and an organicsolvent can be preferably used. Particularly, an aqueous solutionpolymerization method using water as a polymerization solvent ispreferably used.

The weight average molecular weight (Mw) of the water-soluble polymer isnot particularly limited, including the case in which the compound is amorpholine polymer, and it may be, for example, in a range of 10,000 to2,000,000. In some embodiments, the Mw of the water-soluble polymer maybe, for example, 1,500,000 or less, 1,200,000 or less, or 800,000 orless. When the Mw of the water-soluble polymer is smaller, thewater-soluble polymer is more likely to be removed by cleaning. In someembodiments, in order to improve protectivity, the Mw of thewater-soluble polymer may be, for example, 50,000 or more, 100,000 ormore, 200,000 or more, or 300,000 or more, and in some cases, may be400,000 or more, or even 500,000 or more. An LPD reduction effectobtained by applying the art disclosed herein can be effectivelyexhibited even if such a water-soluble polymer having a relatively highMw is used. The number average molecular weight (Mn) of thewater-soluble polymer is, including the case in which the water-solublepolymer is a morpholine polymer, preferably in a range of 1,000 to1,000,000, more preferably in a range of 1,500 to 60,000, and still morepreferably in a range of 2,000 to 400,000. When the number averagemolecular weight (Mn) is 1,000 or more, sufficient surface protectivityof the wafer is secured, and when the Mn is 1,000,000 or less, thedispersibility of the abrasive can be secured. Herein, the weightaverage molecular weight and the number average molecular weight can bemeasured through gel permeation chromatography (GPC, for example,HLC-8220, available from Tosoh Corporation) in terms of polymethylmethacrylate.

The molecular weight distribution (PDI) of the water-soluble polymer isgenerally preferably narrow, including the case in which the compound isa morpholine polymer. Specifically, the value obtained by dividing theweight average molecular weight (Mw) by the number average molecularweight (Mn) is preferably 4.0 or less, more preferably 3.5 or less, andstill more preferably 3.0 or less. When the molecular weightdistribution (PDI) is 4.0 or less, sufficient surface protectivity canbe exhibited, and it is possible to avoid an event that causesdeterioration of dispersibility of the abrasive due to a high molecularweight material.

Although not particularly limited, the content (when two or more typesare included, a total amount thereof) of the water-soluble polymer inthe polishing composition can be, for example, 20 parts by weight orless, with respect to 100 parts by weight of the abrasive. In view ofimproving cleanability and a polishing removal rate, the content of thewater-soluble polymer with respect to 100 parts by weight of theabrasive may be, for example, 10 parts by weight or less, 7 parts byweight or less, 5 parts by weight or less, 4 parts by weight or less, 3parts by weight or less, or 2 parts by weight or less. In view ofimproving surface protectivity of the object to be polished, the contentof the water-soluble polymer with respect to 100 parts by weight of theabrasive may be, for example, 0.01 parts by weight or more, and isgenerally appropriately 0.05 parts by weight or more, and may be 0.1parts by weight or more, 0.5 parts by weight or more, or 1 part byweight or more.

(Polymerization Inhibitor)

A polymerization inhibitor may be added to monomers used forsynthesizing a water-soluble polymer, in order to prevent anunintentional progress of a polymerization reaction during theproduction, transportation, storage, and the like of the monomers. Thepolymerization inhibitor is generally a compound that forms stableradicals by radicals generated in monomers and the like due to light,heat, or the like. Herein, the concept of the polymerization inhibitorin this specification also includes a compound called a polymerizationretarder.

The polymerization inhibitor may be one or two or more selected fromamong known polymerization inhibitors. Examples include a compoundrepresented by the following General Formula (1), a compound representedby the following General Formula (2), a phenothiazine compound, and anitrosamine compound. A water-soluble polymer obtained by using monomerscontaining at least one compound selected from the group consisting of acompound represented by the following General Formula (1), a compoundrepresented by the following General Formula (2), a phenothiazinecompound, and a nitrosamine compound as raw materials can be preferablyused as the water-soluble polymer contained in the polishing compositiondisclosed herein. In such a polishing composition, it is particularlysignificant to limit the content of the reaction product of thepolymerization initiator and the polymerization inhibitor to 0.1 ppb orless of the polishing composition.

Wherein R¹ to R³ each independently represent a hydrogen atom or a groupselected from the group consisting of a hydroxy group, an alkyl grouphaving 1 to 8 carbon atoms and an alkoxy group having 1 to 8 carbonatoms.

Wherein X represents CH₂, CH(CH₂)H_(p)O wherein p is an integer of 0 to3, CHO(CH₂)OH wherein q is an integer of 0 to 3, CHO(CH₂)_(r)CH₃ whereinr is an integer of 0 to 2, CHCOOH, or C═O; and R⁴, R⁵, R⁶ and R⁷ eachindependently represent a group selected from among alkyl groups having1 to 3 carbon atoms.

When R¹ to R³ in General Formula (1) are an alkyl group or an alkoxygroup, the alkyl group included in the alkyl group or alkoxy group maybe linear or branched. The number of carbon atoms of the alkyl group oralkoxy group is preferably about 1 or more and 4 or less, and morepreferably about 1 or more and 3 or less. R¹ preferably represents ahydroxy group.

Examples of compounds represented by General Formula (1) includemethylhydroquinone, t-butylhydroquinone, hydroquinone, methoxyphenol,and the like, 4-tert-butyl pyrocatechol, 2,6-di-tert-butyl-p-cresol andthe like.

Compounds represented by General Formula (2) are knownpiperidine-1-oxyls. Examples of groups that can be selected as R⁴, R⁵,R⁶ and R⁷ include a methyl group, an ethyl group, an n-propyl group, andan isopropyl group. Examples of compounds represented by General Formula(2) include 2,2,6,6-tetramethylpiperidine 1-oxyl,2,2,6,6-tetraethylpiperidine 1-oxyl, 2,2,6,6-tetra-n-propylpiperidine1-oxyl and derivatives thereof.

Examples of phenothiazine compounds include phenothiazine. Examples ofnitrosamine compounds include ammonium N-nitrosophenylhydroxylamine, andN-nitrosophenylhydroxylamine aluminum salts.

The amount of the polymerization inhibitor used is not particularlylimited, and can be, for example, about 0.005 wt % (50 ppm) or more and0.5 wt % (5,000 ppm) or less, and preferably 0.01 wt % (100 ppm) or moreand 0.3 wt % (3.000 ppm) or less with respect to the total weight of allmonomers constituting the whole water-soluble polymer or the weight ofthe water-soluble polymer.

(Polymerization Initiator)

The polymerization is typically performed in the presence of apolymerization initiator. The polymerization initiator is notparticularly limited, and commonly used polymerization initiators can beused. In particular, a radical polymerization initiator is preferablyused.

As the radical polymerization initiator, one or two or more knownradical polymerization initiators can be appropriately selected andused. Examples thereof include persulfates such as sodium persulfate,potassium persulfate and ammonium persulfate, hydroperoxides such ast-butyl hydroperoxide, water-soluble peroxides such as hydrogenperoxide, ketone peroxides such as methyl ethyl ketone peroxide, andcyclohexanone peroxide, dialkyl peroxides such as di-t-butyl peroxideand t-butylcumyl peroxide, oil-soluble peroxides of peroxyesters such ast-butyl peroxypivalate and t-hexyl peroxypivalate, water-soluble azocompounds such as2,2′-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate,2,2′-azobis[2-(2-imidazolin-2-yl)propane],2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride,2,2′-azobis[2-(2-imidazolin-2-yl)propane]disulfate dihydrate,22-azobis(2-amidinopropane)dihydrochloride,2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide],2,2′-azobis(N-butyl-2-methylpropionamide),2,2′-azobis[N-(2-propenyl)-2-methylpropionamide] and4,4′-azobis-4-cyanovaleric acid, and oil-soluble azo compounds such as2,2′-azobisisobutyronitrile, 2,2′-azobis(2,4-dimethylvaleronitrile), and2.2′-azobis(2-methylbutyronitrile).

Among these polymerization initiators, in view of easy control of apolymerization reaction, a water-soluble polymerization initiator suchas persulfates and a water-soluble azo compound can be preferably used.A polymerization initiator which is a water-soluble azo compound isparticularly preferable. The art disclosed herein can be preferablyapplied to a polishing composition containing a water-soluble polymerobtained by using a water-soluble azo compound as a polymerizationinitiator. In such a polishing composition, it is particularlysignificant to limit the content of the reaction product of thepolymerization initiator and the polymerization inhibitor to 0.1 ppb orless of the polishing composition.

The amount of the polymerization initiator used is not particularlylimited, and, for example, preferably a proportion of 0.1 to 10 wt %,more preferably a proportion of 0.1 to 5 wt %, and still more preferablya proportion of 0.2 to 3 wt % of the amount thereof is used with respectto the total weight of monomers used for synthesis of the water-solublepolymer or the weight of the water-soluble polymer.

In synthesizing a water-soluble polymer, as needed, a chain transferagent can be used. With the use of a chain transfer agent, the molecularweight of the water-soluble polymer can be appropriately adjusted. Knownchain transfer agents can be used, and examples thereof includemercaptoacetic acid, mercaptopropionic acid, and 2-mercaptoethanol inaddition to alkyl thiol compounds having an alkyl group having 2 to 20carbon atoms such as ethanethiol, 1-propanethiol, 2-propanethiol,1-butanethiol, 2-butanethiol, 1-hexanethiol, 2-hexanethiol,2-methylheptane-2-thiol, 2-butylbutane-1-thiol,1,1-dimethyl-1-pentanethiol, 1-octanethiol, 2-octanethiol,1-decanethiol, 3-decanethiol, I-undecanethiol, 1-dodecanethiol,2-dodecanethiol, 1-tridecanethiol, 1-tetradecanethiol,3-methyl-3-undecanethiol, 5-ethyl-5-decanethiol, tert-tetradecanethiol,1-hexadecanethiol, 1-heptadecanethiol and 1-octadecanethiol. These canbe used singly or in a combination of two or more.

The reaction temperature (polymerization temperature) at which awater-soluble polymer is synthesized from monomers is preferably 30° C.to 100° C., more preferably 40° C. to 90° C., and still more preferably50° C. to 80° C. In view of suppressing generation of the reactionproduct of the polymerization initiator and the polymerizationinhibitor, synthesis of the water-soluble polymer is preferablyperformed under a non-oxygen atmosphere and, for example, it ispreferably performed under an inert gas such as nitrogen gas.

(Reaction Product of Polymerization Initiator and PolymerizationInhibitor)

In the polishing composition disclosed herein, the content of thereaction product of the polymerization initiator and the polymerizationinhibitor is 0.1 ppb or less with respect to the polishing composition.

In a system in which a polymerization initiator and a polymerizationinhibitor coexist, in the presence of oxygen, the reaction product ofthe polymerization initiator and the polymerization inhibitor isgenerated from radicals derived from the polymerization initiator. Forexample, one reaction scheme is shown below. The following scheme 1 isan inference and example, and is not intended to limit the disclosure ofthis specification, and shows an example in which the polymerizationinitiator is 2,2′-azobis[2-(2-imidazolin-2-yl)propane]disulfatedehydrate which is one of radical polymerization initiators and thepolymerization inhibitor is MQ (hydroquinone monomethyl ether). From acombination of the polymerization initiator and the polymerizationinhibitor, in the presence of oxygen, for example, it is thought thatthe following compound a is generated as the reaction product.

[C3]

In the scheme 1, radicals derived from the polymerization initiator aregenerated. For example, in the presence of oxygen, radicals of thepolymerization initiator may react with oxygen to generatepolymerization initiator-oxygen radicals. Such radicals can extractprotons from the polymerization inhibitor to generate polymerizationinhibitor radicals. It is thought that the polymerization inhibitorradicals couple with polymerization initiator-oxygen radicals orpolymerization initiator radicals to generate the compound a as acoupling reaction product at a molar ratio of 1:1.

Radicals of the polymerization initiator and radicals of thepolymerization inhibitor can cause various other reactions. For example,polymerization inhibitor radicals react with other polymerizationinhibitors in a chain reaction to generate a chain reaction product ofthe polymerization inhibitor.

In this manner, the reaction product may include various reactionproducts such as a coupling reaction product of a polymerizationinitiator and a polymerization inhibitor and a chain reaction product ofa polymerization inhibitor. Accordingly, the reaction product can be amixture of a wide variety of compounds. In one embodiment of the artdisclosed herein, the compound can be a reaction product in which apolymerization initiator and a polymerization inhibitor are coupled viaoxygen. The compound a is exemplified as the coupled reaction product.In one embodiment of the art disclosed herein, measurement of the amountof the reaction product can be replaced by measurement of the amount ofthe compound a. The amount of the compound a can be measured throughliquid chromatography (LC) or the like. It can also be calculated fromthe amounts of the initiator and the inhibitor reduced with respect tothe initial amounts.

It is thought that the reaction product includes the above-describedreaction products derived from the polymerization initiator and thepolymerization inhibitor. Such a reaction product includes a structurederived from a polymerization inhibitor. Therefore, for example,generally, it is thought to be a hydrophobic compound having an aromaticring derived from a polymerization inhibitor or a hydrophobic moietyderived from a heterocyclic amine. It is thought that this reactionproduct constitutes a solute part having relatively high hydrophobicityin a polishing composition containing water and a water-soluble polymer.The highly hydrophobic reaction product is likely to be adsorbed on thesurface of an object to be polished such as a wafer whose surface ishydrophobic. Therefore, this reaction product is not removed by cleaningafter polishing but is likely to remain on the surface of the object tobe polished, and as a result, it can be detected as LPDs.

According to the an disclosed herein, by suppressing the amount of thereaction product with respect to the polishing composition to 0.1 ppb orless, it is possible to effectively reduce LPDs caused by adsorption ofthe reaction product to the surface of the object to be polished. Inview of improving the LPDs reduction effect, in some embodiments, theamount of the reaction product may be, for example, 0.05 ppb or less,0.02 ppb or less, or 0.01 ppb or less. In consideration of handlingproperties of monomers used as a raw material of the water-solublepolymer, productivity and handling properties of the water-solublepolymer, and productivity of the polishing composition, and the like, insome embodiments, the polishing composition includes the reactionproduct. The amount of the reaction product may be 0.001 ppb or more or0.005 ppb or more.

The amount of the reaction product contained in a polishing compositioncan be adjusted by, for example, the amount of the reaction product thatthe water-soluble polymer used for preparing the polishing compositioncontains. The amount of the reaction product with respect to thewater-soluble polymer may vary depending on the type and amount of thepolymerization inhibitor contained in the monomers used for synthesis ofthe water-soluble polymer, the type of the polymerization initiator andthe amount of the polymerization initiator used with respect tomonomers, the concentration of the polymerization inhibitor and thepolymerization initiator in a mixture in which the polymerizationinhibitor and the polymerization initiator coexist, a time for which thecoexisting state continues and the temperature of the mixture during thetime, the amount of oxygen contained in the mixture or in contact withthe mixture, or the like. For example, the amount of the reactionproduct with respect to the water-soluble polymer tends to be reduced byreducing the amount of a polymerization initiator used, using apolymerization initiator with a higher decomposition rate, usingmonomers with a lower content of a polymerization inhibitor or monomersthat have been subjected to a purification treatment for removing a partor all of the polymerization inhibitor immediately before use, synthesisof a water-soluble polymer at a lower concentration (that is, using alarge amount of a polymerization solvent), synthesis of a water-solublepolymer which more strictly excludes the incorporation of oxygen andcontact with oxygen, reducing a polymerization temperature, shortening apolymerization time, by performing a treatment for decomposing thepolymerization initiator remaining after polymerization by heatingand/or elapse of time, or purifying a water-soluble polymer byreprecipitation or the like. Those skilled in the art can reduce theamount of the reaction product with respect to the water-soluble polymerwithout an excessive burden by appropriately using one or two or moremethods including these exemplified methods. Thus, a polishingcomposition in which the amount of the reaction product with respect tothe polishing composition is 0.1 ppb or less or within a preferablerange disclosed herein can be obtained without an excessive burden.

A coupling reaction product in which the molar ratio between thepolymerization initiator and the polymerization inhibitor is 1:1 can bedetected by performing liquid chromatography based on liquidchromatography of a polymerization inhibitor to be described below, andalso the concentration of the coupling reaction product can bequantified.

In addition, including the coupling reaction product, the concentrationof the reaction product can be acquired as an estimated amount using theamount of the polymerization inhibitor reduced before and after thereaction, that is, a difference between the concentration before thereaction and the concentration after the reaction. More specifically,the amount of the reaction product generated is estimated by estimatingthat the amount of the polymerization inhibitor decreased is completelyconsumed by the coupling reaction between the polymerization initiatorand the polymerization inhibitor at a ratio of 1:1. For example, theconcentration of the reaction product with respect to the water-solublepolymer is estimated from the concentration of the polymerizationinhibitor contained in the water-soluble polymer before and after thereaction with the polymerization initiator as follows.

Concentration of the reaction product with respect to water-solublepolymer=(concentration of polymerization inhibitor with respect towater-soluble polymer before reaction−concentration of thepolymerization inhibitor after reaction)×estimated molecular weight ofthe coupling reaction product/molecular weight of polymerizationinhibitor.

For example, in the above scheme 1, the molecular weight of thepolymerization inhibitor is 128, and the molecular weight of thecoupling reaction product obtained by the reaction between thepolymerization initiator and the polymerization inhibitor at a molarratio of 1:1 is 383. The concentration and amount of the generatedreaction product can be estimated based on such molecular weightinformation and the amount of the polymerization inhibitor decreased.Here, those skilled in the art can understand a coupling reactionproduct including the polymerization initiator and the polymerizationinhibitor at a molar ratio of 1:1 from respective structures of thepolymerization initiator and the polymerization inhibitor based on thescheme 1 and common technical knowledge and can calculate its molecularweight.

In addition, for example, from a combination of ammonium persulfate asthe polymerization initiator and MQ (hydroquinone monomethyl ether) asthe polymerization inhibitor, the following one coupling reactionproduct is estimated according to the following scheme 2.

In addition, for example, from a combination of2,2′-azobis[2-(2-imidazolin-2-yl)propane]disulfate dihydrate) as apolymerization initiator and phenothiazine as a polymerizationinhibitor, the following one coupling reaction product will beestimated.

In addition, it has been found that the water-soluble polymer is coloredfrom light yellow to yellowish brown depending on the content of thereaction product with respect to the water-soluble polymer. For example,the concentration of the reaction product can be estimated using such adegree of coloring obtained by measuring a yellowness index (YI) as anindex. For example, YI can be obtained by performing measurement on anaqueous solution in which the solid content of the water-soluble polymeris adjusted to 20 wt % using OME-2000 (available from Nippon DenshokuIndustries Co., Ltd.) or a device capable of measuring YI with the sameprecision and accuracy according to JIS K 7373.

<Basic Compound>

The basic compound is not particularly limited, and various known basiccompounds used as polishing compositions for object to be polished suchas wafers can be used. Such a basic compound may be any water-solublebasic compound, and one or two or more selected from among knowninorganic basic compounds and organic basic compounds can beappropriately selected and used.

Examples of inorganic basic compounds include ammonia, and hydroxides,carbonates, and bicarbonates of alkali metals and alkaline earth metals.Examples of hydroxides include potassium hydroxide, sodium hydroxide,rubidium hydroxide and cesium hydroxide. Examples of carbonates andbicarbonates include ammonium bicarbonate, ammonium carbonate, potassiumbicarbonate, potassium carbonate, sodium bicarbonate, and sodiumcarbonate.

Examples of organic basic compounds include amines, ammonia, andquaternary ammonium hydroxide salts. Examples of amines includetriethylamine, monoethanolamine, diethanolamine, triethanolamine,diisopropanolamine, ethylenediamine, hexamethylenediamine,diethylenetriamine, triethylpentamine and tetraethylpentamine. Examplesof quaternary ammonium hydroxide salts include tetramethylammoniumhydroxide, tetraethylammonium hydroxide and tetrabutylammoniumhydroxide. For example, in view of low contamination on a semiconductorsubstrate, ammonia and/or quaternary ammonium hydroxide salts can bepreferably used. The content of the basic compound in the composition isappropriately set. With the addition of such a basic compound or thelike, the composition disclosed herein preferably has a pH of 8 to 13,at least at a time the composition is subjected to a polishing process.The range of pH is more preferably adjusted to 8.5 to 12, and still morepreferably adjusted to 9.5 to 11.0.

<Water>

Regarding water in the composition, ion exchange water (deionizedwater), pure water, ultrapure water, distilled water, or the like can bepreferably used. In order to avoid impairing the effect of othercomponents contained in the polishing composition as much as possible,for example, the total content of transition metal ions in the water tobe used is preferably 100 ppb or less For example, the purity of watercan be improved by operations such as removal of impurity ions using anion exchange resin, removal of contaminants using a filter, anddistillation. As will be described below, the composition disclosedherein may further contain as needed an organic solvent (lower alcohol,lower ketone, etc.) that can be uniformly mixed with water. Generally,preferably 90 volume % or more of the solvent contained in the polishingcomposition is water, and more preferably 95 volume % or more (typically99 to 100 volume %) thereof is water.

<Other Components>

In addition, the composition can appropriately include, as optionalcomponents, known additives that can be used in the polishingcomposition. Examples include various chelating agents, surfactants,preservatives, and antifungal agents in addition to the organic solventsdescribed above. The chelating agent has a function of forming complexions with metal impurities that can be contained in the polishingcomposition and capturing them and thus suppressing contamination of anobject to be polished due to metal impurities. As the chelating agent,known chelating agents can be used singly or in a combination of two ormore. The surfactant is not particularly limited, for example, one ortwo or more selected from among known anionic or nonionic surfactantscan be appropriately selected and used.

Preferably, the composition disclosed herein is substantially free of anoxidizing agent. In case an oxidizing agent is contained, for example,the surface of the object to be polished such as a wafer is oxidized toform an oxide layer with the supply of this composition, and thereby thepolishing removal rate can decrease. Specific examples of oxidizingagents include hydrogen peroxide (H₂O₂), sodium persulfate, ammoniumpersulfate, and sodium dichloroisocyanurate. Herein, when it is statedthat the composition is substantially free of an oxidizing agent, itmeans that an oxidizing agent is not contained at least intentionally.

The form of the composition is not particularly limited. For example,the composition may be in a form of a polishing liquid (working slurry)that is supplied to an object to be polished in a polishing process asis. In addition, the composition may be in a form of a polishing stocksolution that is generally diluted with water or a liquid mixture ofwater and an organic solvent at the time of use. The polishing stocksolution can be understood as a concentrate of a working slurry. Inaddition, the composition may be in a form of a kit in which thecomponents constituting the composition are mixed at the time of use.That is, the composition may be in a form of a kit in which a pluralityof agents each contains one or two or more components among awater-soluble polymer, a reaction product, an abrasive and a basiccompound are combined. As will be described below, one agent among theplurality of agents may be a polymer composition containing awater-soluble polymer. The kit can further include one or two or moreoptional components in addition to water.

The pH of the polishing liquid is preferably adjusted to, for example,about 8 or more 13 or less. For example, the pH is preferably 8.5 ormore or 9.0 or more, and more preferably 9.5 or more or 10.0 or more.The pH is, for example, preferably 12.5 or less or 12.0 or less, andmore preferably 11.5 or less or 11.0 or less.

The composition can be produced by, for example, a method includingpreparing a polymer composition which includes the water-soluble polymerand in which the content of the reaction product is 0.1 ppb or less ofthe polishing composition, and mixing the polymer composition, theabrasive, and the basic compound. The polymer composition may be acomposition in a form in which a water-soluble polymer is dissolved inwater, that is, an aqueous solution of a water-soluble polymer. As thepolymer composition, for example, a polymerization reaction liquidobtained from the synthesis of a water-soluble polymer, or thoseobtained by subjecting one or more treatments such as dilution,concentration, drying, neutralization, and adding optional components onthe polymerization reaction liquid can be used. Alternatively, thoseobtained by purifying a water-soluble polymer contained in thepolymerization reaction liquid using known methods such as filtration,adsorption, and reprecipitation may be used as the polymer composition.

When components are mixed to provide the composition, the mixing orderand the mixing method are not particularly limited. The components maybe independently mixed in any order, or two or more components may beappropriately mixed in advance and all components may be then mixed. Themixing method is not particularly limited, and known mixing devices, forexample, well-known mixing devices such as a wing type stirrer, anultrasonic dispersing machine, and a homo mixer can be used.

<Applications>

The composition disclosed herein can be applied for polishing of objectsto be polished having various materials and shapes. Examples ofmaterials of objects to be polished include metals or metalloids such assilicon, aluminum, nickel, tungsten, copper, tantalum, titanium, andstainless steel, or alloys thereof: glassy materials such as quartzglass, aluminosilicate glass, glassy carbon, or the like; ceramics suchas alumina, silica, sapphire, silicon nitride, tantalum nitride, andtitanium carbide; compound semiconductor substrate materials such assilicon carbide, gallium nitride, and gallium arsenide; resin materialssuch as a polyimide resin; and the like. An object to be polished may beformed of a plurality of materials among these.

The composition disclosed herein can be particularly preferably used forpolishing a surface made of silicon such as silicon substrate. A typicalexample of the silicon substrate here is a single crystal silicon wafer,and is, for example, a single crystal silicon wafer obtained by slicinga single crystal silicon ingot.

The composition disclosed herein can be preferably applied to apolishing step of an object to be polished, for example, a polishingstep of a silicon wafer. Before a polishing step using this composition,a general treatment that can be applied to an object to be polished in astep upstream from the polishing step such as lapping and etching can beapplied to the object to be polished.

The composition disclosed herein can be preferably used for, forexample, polishing of an object to be polished whose surface is adjustedto a surface roughness of 0.01 nm to 100 nm in the upstream step, forexample, polishing a wafer. The surface roughness Ra of the object to bepolished can be measured using, for example, a laser scan surfaceroughness meter “TMS-3000WRC” available from Schmitt Measurement SystemInc. Use in final polishing (finish polishing) or polishing immediatelytherebefore is effective, and use in final polishing is particularlypreferable. Herein, the final polishing refers to the last polishingstep in a process of producing an object, that is, a step in which noadditional polishing is performed after that step.

<Polishing>

The composition disclosed herein can be used for polishing an object tobe polished, for example, in an embodiment including the followingoperations. Hereinafter, a preferable embodiment of a method forpolishing an object to be polished using this composition, for example,a silicon wafer, will be described.

That is, a polishing liquid containing any of the polishing compositionsdisclosed herein is prepared. Preparing of the polishing liquid mayinclude preparing a polishing liquid by performing operations such asadjustment of a concentration such as dilution and adjustment of the pHon the polishing composition. Alternatively, the polishing compositionmay be directly used as a polishing liquid.

Next, the polishing liquid is supplied to an object to be polished andthe object is polished by a general method. For example, when finalpolishing is performed on a silicon wafer, typically, a silicon waferhaving undergone a lapping step is set in a general polishing machine,and a polishing liquid is supplied to a surface to be polished of thesilicon wafer through a polishing pad of the polishing machine.Typically, while the polishing liquid is continuously supplied, thepolishing pad is pressed against a surface to be polished of the siliconwafer, and they are moved relatively, for example, rotated. Polishing ofthe object to be polished is completed through such a polishing step.

The polishing pad used in the polishing step is not particularlylimited. For example, polyurethane foam type, non-woven fabric type, andsuede type polishing pads can be used. The polishing pads may or may notcontain an abrasive. Generally, a polishing pad containing no abrasiveis preferably used.

Matters disclosed herein include the followings.

[1] A polishing composition including:

an abrasive;

a water-soluble polymer; and

a basic compound,

wherein a content of a reaction product of a polymerization initiatorand a polymerization inhibitor is 0.1 ppb or less of the polishingcomposition on a weight basis.

[2] The polishing composition according to [1] above, wherein thepolymerization inhibitor includes at least one compound selected fromthe group consisting of a compound represented by the following GeneralFormula (1), a compound represented by the following General Formula(2), a phenothiazine compound, and a nitrosamine compound:

wherein R¹ to R³ each independently represent a hydrogen atom or a groupselected from the group consisting of a hydroxy group, an alkyl grouphaving 1 to 8 carbon atoms and an alkoxy group having 1 to 8 carbonatoms,

wherein X represents CH₂, CH(CH₂)_(p)OH wherein p is an integer of 0 to3, CHO(CH₂)_(q)OH wherein q is an integer of 0 to 3, CHO(CH)_(r)CH₃wherein r is an integer of 0 to 2, CHCOOH, or C═O; and R⁴, R⁵, R⁶ and R⁷each independently represent a group selected from among alkyl groupshaving 1 to 3 carbon atoms.

[3] The polishing composition according to [1] or [2] above, wherein thewater-soluble polymer contains 10 mol % or more and 100 mol % or less ofa structural unit derived from a monomer containing a nitrogen atom.[4] The polishing composition according to any of [1] to [3] above, usedfor polishing a silicon wafer.[5] A method for producing the polishing composition according to any of[1] to [4] above, the method including:

preparing a polymer raw material containing the water-soluble polymer,wherein a content of the reaction product in the polymer raw material is0.1 ppb or less with respect to the polishing composition on a weightbasis; and

mixing the polymer raw material, the abrasive, and the basic compound.

EXAMPLES

Several Examples relating to the present invention are described belowalthough the present invention is not to be limited to such Examples.Hereinafter, unless otherwise specified. “parts” and “%” refer to “partsby weight” and “% by weight.” A method for analyzing water-solublepolymers obtained in production examples, water-soluble polymers(hereinafter simply referred to as a polymer) in examples andcomparative examples, and a method for evaluating a polishingcomposition will be described below.

(1) Measurement of Molecular Weight

The molecular weight of each polymer was measured through gel permeationchromatography (GPC) under the following conditions, and determined as aweight average molecular weight (Mw) in terms of polymethylmethacrylate.

[Measurement Conditions]

Device: HLC-8320GPC (available from Tosoh Corporation)Column: TSKgel SuperHM-Mx3 columns (available from Tosoh Corporation)Solvent: N,N-dimethylformamide (containing 10 mM LiBr)

Temperature: 40° C. Detector: RI

Flow rate: 300 μL/min

(2) Measurement of Amount of Polymerization Inhibitor and Estimation ofAmount of Reaction

Product 15 mg of the polymer obtained in the production example wascollected in a 2 mL micro tube, 1 mL of methanol was added thereto, andthe mixture was stirred using a shaker for 30 min. Then, a supernatantliquid was collected using a centrifuge (12,000×5 min), and measurementwas performed through liquid chromatography (LC) under the followingconditions. The amount of the polymerization inhibitor contained in thepolymer was calculated from a peak area derived from the polymerizationinhibitor.

[Measurement Conditions]

Device: LC-20AC+SPD-M20A (available from Shimadzu Corporation)Column: Inertsil ODS-3 (available from GL Sciences Inc.)Solvent: water/methanol=45/55 wt % (constant gradient)

Temperature: 40° C.

Detection wavelength: 290 nmFlow rate: 300 μL/min

N-acryloylmorpholine used in the production examples contained 1,000 ppmof MQ (methoxyphenol, molecular weight of 128) as the polymerizationinhibitor with respect to monomers. A radical coupling reaction productincluding radicals of 2.2′-azobis[2-(2-imidazolin-2-yl)propane]disulfatedehydrate (VA-046B available from Wako Pure Chemical Industries. Ltd) asthe polymerization initiator and radicals of MQ at a ratio of 1/1 wasestimated as follows, and its molecular weight was set to 383, and theamount of the reaction product was calculated.

Production of Polymer Production Example 1

Pure water (390 g) was put into a 1 L flask equipped with a stirrer, areflux cooling pipe, a thermometer and a nitrogen (or 5% oxygen (basedon volume)) inlet pipe. While bubbling nitrogen gas blown into the purewater from the nitrogen inlet pipe (100 ml/min), the system was heatedto 90° C. and stirred at the same temperature for 30 minutes. Thereby,oxygen dissolved in the pure water was removed. Next, while continuingnitrogen bubbling, the system was cooled to 60° C., and2,2′-azobis[2-(2-imidazolin-2-yl)propane]disulfate dehydrate (VA-046B,available from Wako Pure Chemical Industries, Ltd., 0.35 g) was addedthereto. Here, N-acryloylmorpholine (ACMO, available from KJ ChemicalsCorporation, 100 g) was added dropwise thereto over 3 hours andpolymerized. After dropwise addition as completed, stirring wasperformed at 60° C. while additionally continuing nitrogen bubbling for1 hour. The system was then heated to 80° C. and stirred for 2.5 hourswhile performing nitrogen bubbling, thereby the remaining polymerizationinitiator was decomposed under a non-oxygen atmosphere to reduce theamount thereof. Then, nitrogen bubbling was stopped, the system wasopened, and was cooled to room temperature. Then, switched to 5% oxygenbubbling (50 ml/min), an initiator treatment in which stirring for 30days under an internal temperature adjusted to 40 C was performed. Apolymerization reaction liquid A as a polymer A aqueous solution wasthus obtained.

Here, 4 hours after (that is, immediately before the system was heatedto 80° C.) from when dropwise addition of ACMO started, a part of thereaction liquid was taken out and analyzed, and it was confirmed thatthe polymerization conversion of ACMO at that time was about 100%. Inthis reaction liquid, with respect to the amount of ACMO used, theamount of the polymerization inhibitor was 1.000 ppm before theinitiator treatment, and 999.90 ppm after the initiator treatment, andthe amount of the compound a estimated from the amount of thepolymerization inhibitor reduced (0.10 ppm) was 0.30 ppm with respect tothe amount of ACMO used.

Production Example 2

A polymerization reaction liquid B as a polymer B aqueous solution wasobtained in the same manner as in Production Example 1 except that theamount of the polymerization initiator used was changed to 0.15 g inProduction Example 1. The amount of the polymerization inhibitor reducedwas 0.04 ppm, and the amount of compound a estimated from the amount ofthe polymerization inhibitor reduced was 0.13 ppm with respect to theamount of ACMO used.

200 g of a liquid in Production Example 1 which is after polymerizationand immediately after stirring under nitrogen bubbling at 80° C. for 2.5hours (i.e., the liquid before the initiator treatment), 0.24 g of thepolymerization initiator (VA-046B), 0.392 g of the polymerizationinhibitor (MQ), and 10 g of water were mixed and the mixture was heatedand stirred at 50° C. for 3 days. The liquid obtained from the aboveoperation was referred to as a “stock liquid.”

The amount of the polymerization inhibitor in the stock liquid withrespect to ACMO was 9607.2 ppm before heating and stirring, and 8080.4ppm after heating and stirring, and the amount of compound a estimatedfrom the amount of the polymerization inhibitor reduced was 4,700 ppmwith respect to the amount of ACMO used.

Preparation of Polishing Liquid Example 1

The polymerization reaction liquid A was mixed with an abrasive, ammoniawater (concentration of 29%) and deionized water to obtain a polishingcomposition concentrate. The concentrate was diluted by a factor of 20with deionized water to prepare a polishing liquid (working slurry).

Here, as the abrasive, colloidal silica having an average primaryparticle size of 35 nm and an average secondary particle size of 60 nmwas used. The average primary particle size was measured using a surfacearea measuring device (product name “Flow Sorb II 2300” available fromMicromeritics Instrument Corporation). The average secondary particlesize was a volume average particle size based on a dynamic lightscattering method measured using a model “UPA-UT151” (available fromNikkiso Co., Ltd.).

Regarding the used amounts of the abrasive, polymerization reactionliquid A and ammonia water, the content of the abrasive in the polishingliquid was 0.46%, the content of the polymer A was 0.0075%, and thecontent of ammonia was 0.01%.

Example 2

A polishing liquid according to Example 2 was prepared in the samemanner as in Example 1 except that the polymerization reaction liquid Bwas used in place of the polymerization reaction liquid A in Example 1.

Comparative Examples 1 and 2

Polishing liquids according to Comparative Examples 1 and 2 wereprepared in the same manner as in Example 1 except that liquids obtainedby mixing the polymerization reaction liquid A and the stock liquid atratios shown in Table 1 were used in place of the polymerizationreaction liquid A in Example 1.

<Polishing Test> (Polishing of Silicon Wafer)

Using the polishing liquids according to respective examples, a siliconwafer was polished under the following conditions. As the silicon wafer,those obtained by preliminary polishing a lapped and etched commercialsilicon single crystal wafer (P-type conductivity, crystal orientation:<100>, resistivity: 1 Ω·cm or more and less than 100 Ω·cm, COP free)with a diameter of 200 mm to adjust the surface roughness to 0.1 nm to10 nm was used. For the preliminary polishing, a preliminary polishingslurry containing 0.95% of colloidal silica having an average primaryparticle size of 35 nm and 0.065% of potassium hydroxide in water wasused.

[Polishing Conditions]

Polishing machine: single wafer polishing machine, model “PNX-332B”(available from Okamoto Machine Tool Works. Ltd.)Polishing table: the first and second stages of final polishing afterpreliminary polishing were performed using the latter two tables amongthree tables of the polishing machine.(The following conditions were the same for the tables)Polishing pressure: 15 kPaPlaten rotational speed: 30 rpmHead rotational speed: 30 rpmPolishing time: 2 minutesTemperature of polishing liquid: 20° C.Flow rate of polishing liquid: 2.0 L/min (one-way)

(Cleaning)

The silicon wafer after polishing was cleaned using a cleaning solutioncontaining NH₄OH (29%):H₂O₂ (31%):deionized water (DIW)=1:3:30 (volumeratio) (SC-1 cleaning). More specifically, two cleaning baths equippedwith an ultrasonic wave oscillator of 950 kHz frequency were prepared,the cleaning solution was placed in each of the first and secondcleaning baths and maintained at 60° C., the silicon wafer afterpolishing was immersed in the first cleaning bath for 6 minutes, passedthrough a rinse bath with ultrapure water and ultrasonic waves, andimmersed in the second cleaning bath for 6 minutes while the ultrasonicwave oscillators were turned on.

(Evaluation of LPDs)

The number of defects with a size of 61 nm or more present on thesurface of the silicon wafer after cleaning was counted using a waferdefect tester (product name “Surfscan SP2XP” available from KLA-Tencor).The result was converted into a relative value with respect to 100% ofComparative Example 1, and evaluated according to the followingthree-grade scale. The results are shown in Table 1.

I: Relative value with respect to Comparative Example 1 was 90% or lessII: Relative value with respect to Comparative Example 1 was more than90% and 120% or lessIII: Relative value with respect to Comparative Example 1 was more than120%

TABLE 1 Content of Polymer reaction (Mw) Composition product [ppb] LPDsExample 1 A (325,000) Polymerization 0.02 I reaction liquid A Example 2B (560,000) Polymerization 0.01 I reaction liquid B Comparative A(325,000) Polymerization 0.29 II Example 1 reaction liquid A:stockliquid = 99.92%:0.080% Comparative A (325,000) Polymerization 1.33 IIIExample 2 reaction liquid A:stock liquid = 99.61%:0.39%

As shown in Table 1, it was confirmed that LPDs were significantlyreduced in Examples 1 and 2 in which the amount of the reaction productwith respect to the polishing composition was 0.1 ppb or less comparedto Comparative Examples 1 and 2 in which the amount of the reactionproduct was more than 0.1 ppb.

While specific examples of the present invention have been describedabove in detail, these are only examples, and do not limit the scope ofthe claims. The technologies described in the scope of the claimsinclude various modifications and alternations of the specific examplesexemplified above.

1. A polishing composition comprising: an abrasive; a water-solublepolymer; a basic compound; and a reaction product of a polymerizationinitiator and a polymerization inhibitor; wherein a content of thereaction product of the polymerization initiator and the polymerizationinhibitor is 0.1 ppb or less of the polishing composition on a weightbasis, and the water-soluble polymer contains 10 mol % or more and 100mol % or less of a structural unit derived from a monomer containing anitrogen atom.
 2. The polishing composition according to claim 1,wherein the polymerization inhibitor includes at least one compoundselected from the group consisting of a compound represented by thefollowing General Formula (1), a compound represented by the followingGeneral Formula (2), a phenothiazine compound, and a nitrosaminecompound:

wherein R¹ and R² each independently represent a hydrogen atom or agroup selected from the group consisting of a hydroxy group, an alkylgroup having 1 to 8 carbon atoms and an alkoxy group having 1 to 8carbon atoms, and R³ represents a group selected from the groupconsisting of an alkyl group having 1 to 8 carbon atoms and an alkoxygroup having 1 to 8 carbon atoms;

wherein X represents CH₂, CH(CH₂)_(p)OH wherein p is an integer of 0 to3, CHO(CH₂)_(q)OH wherein q is an integer of 0 to 3, CHO(CH₂)_(r)CH₃wherein r is an integer of 0 to 2, CHCOOH, or C═O; and R⁴, R⁵, R⁶ and R⁷each independently represent a group selected from among alkyl groupshaving 1 to 3 carbon atoms.
 3. The polishing composition according toclaim 1, wherein the amount of the polymerization inhibitor used is0.005 wt % or more and 0.5 wt % or less with respect to the weight ofthe water-soluble polymer.
 4. A method of polishing a silicon wafercomprising, polishing the silicon wafer with a polishing composition ofclaim
 1. 5. A method for producing the polishing composition accordingto claim 1, the method comprising: preparing a polymer compositioncontaining the water-soluble polymer, wherein the content of thereaction product in the polymer composition is 0.1 ppb or less withrespect to the polishing composition on a weight basis; and mixing thepolymer composition, the abrasive, and the basic compound.
 6. Thepolishing composition according to claim 2, wherein the content of thereaction product of the polymerization initiator and the polymerizationinhibitor is 0.001 ppb or more and 0.1 ppb or less of the polishingcomposition on a weight basis.
 7. The polishing composition according toclaim 1, wherein the polymerization inhibitor includes at least onecompound selected from the group consisting of a compound represented bythe following General Formula (1), a compound represented by thefollowing General Formula (2), a phenothiazine compound, and anitrosamine compound:

wherein R¹ to R³ each independently represent a hydrogen atom or a groupselected from the group consisting of a hydroxy group, an alkyl grouphaving 1 to 8 carbon atoms and an alkoxy group having 1 to 8 carbonatoms,

wherein X represents CH₂, CH(CH₂)_(p)OH wherein p is an integer of 0 to3, CHO(CH₂)_(q)OH wherein q is an integer of 0 to 3, CHO(CH₂)_(r)CH₃wherein r is an integer of 0 to 2, CHCOOH, or C═O; and R⁴, R⁵, R⁶ and R⁷each independently represent a group selected from among alkyl groupshaving 1 to 3 carbon atoms, wherein the polymerization initiator is aradical polymerization initiator, wherein the radical polymerizationinitiator is one or two or more selected from the group consisting ofpersulfates, water-soluble peroxides, oil-soluble peroxides,water-soluble azo compounds and oil-soluble azo compounds, and whereinthe reaction product of a polymerization initiator and a polymerizationinhibitor is a coupling reaction product of the polymerization initiatorand the polymerization inhibitor.
 8. The polishing composition accordingto claim 7, wherein the amount of the polymerization inhibitor used is0.005 wt % or more and 0.5 wt % or less with respect to the weight ofthe water-soluble polymer.
 9. The polishing composition according toclaim 7, wherein the content of the reaction product of thepolymerization initiator and the polymerization inhibitor is 0.001 ppbor more and 0.1 ppb or less of the polishing composition on a weightbasis.
 10. The polishing composition according to claim 1, wherein thepolymerization initiator is a radical polymerization initiator, whereinthe radical polymerization initiator is one or two or more selected fromthe group consisting of persulfates, water-soluble peroxides,oil-soluble peroxides, water-soluble azo compounds and oil-soluble azocompounds, and wherein the reaction product of a polymerizationinitiator and a polymerization inhibitor is a coupling reaction productof the polymerization initiator and the polymerization inhibitor. 11.The polishing composition according to claim 1, wherein thewater-soluble polymer is a morpholine polymer having a structural unitderived from N-(meth)acryloylmorpholine.
 12. The polishing compositionaccording to claim 11, wherein the morpholine polymer has a weightaverage molecular weight of 200,000 or more.
 13. The polishingcomposition according to claim 1, wherein the abrasive is colloidalsilica having an average secondary particle size of 35 nm or more. 14.The polishing composition according to claim 13, wherein the abrasivehas an average aspect ratio of 1.0 or more and 1.5 or less.